As a water supply method, there are a direct coupling method in which water is directly supplied by a water main pipe, and a water receiving tank method in which water supplied by a water main pipe is received by a water receiving tank. In a case in which a building has many stories, or in which a large amount of water is used at a time, water receiving tank-type water supply is performed in which a water receiving tank is installed for supplying water. The water receiving tank-type water supply is a method in which water from a water pipe is temporarily received by a water receiving tank and water is supplied from the water receiving tank. It is possible to maintain a constant water supply pressure and a constant water supply amount even when a water pressure of a water supply pipe changes, to use a large amount of water at a time, and to further ensure water supply even at the time of water outage or disaster.
In a case in which water supplied from a water supply source is heated and supplied, a hot water supply device is used in which a hot water storage tank is connected to the water receiving tank and hot water is supplied from the hot water storage tank (for example, see Patent Literatures 1 and 2). Patent Literature 1 discloses a heat pump hot water supply device in which two hot water storage tanks connected via a pipe are provided, and a low temperature-side heat pump hot water supplier and a high temperature-side heat pump hot water supplier are respectively connected to the hot water storage tanks. Warm water heated in the low temperature-side heat pump hot water supplier is transferred from one of the hot water storage tanks to the other of the hot water storage tanks through the pipe. The warm water in the other hot water storage tank is heated by the high temperature-side heat pump hot water supplier.
Patent Literature 2 discloses a hot water supply device in which a water supply source and a cushion tank are connected to a hot water storage tank. A heat pump hot water supplier is connected to the cushion tank. A controller controls whether water from the water supply source or warm water in the cushion tank heated by the heat pump hot water supplier is supplied to the hot water storage tank based on an outside air temperature and an inflow water temperature.